Method of producing beraprost

ABSTRACT

An improved method is described for making single isomers of synthetic benzoprostacyclin analogue compounds, in particular the pharmacologically active 314-d isomer of beraprost. In contrast to the prior art, the method is stereoselective and requires fewer steps than the known methods for making these compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.14/645,715, filed Mar. 12, 2015, which is a Divisional of U.S.application Ser. No. 14/294,384, filed Jun. 3, 2014, which is aDivisional of U.S. application Ser. No. 13/524,568, filed Jun. 15, 2012,now U.S. Pat. No. 8,779,170, which issued on Jul. 15, 2014, claimspriority from U.S. Provisional Application No. 61/497,754, filed Jun.16, 2011, the entirety of which is incorporated herein by reference.

FIELD

The present application relates to a process for selectively producingsingle-isomer benzoprostacyclin derivatives including beraprost and itsderivatives. The present invention also relates to a novel process forattaching the alpha side-chain to single-isomer key intermediate leadingto beraprost and related derivatives.

BACKGROUND OF THE INVENTION

Prostacyclin derivatives are useful pharmaceutical compounds possessingactivities such as platelet aggregation inhibition, gastric secretionreduction, lesion inhibition, and bronchodilation. Beraprost is asynthetic benzoprostacyclin analogue of natural prostacyclin that iscurrently under clinical trials for the treatment of pulmonaryhypertension and vascular disease (excluding renal disease) in NorthAmerica and Europe.

Beraprost and related benzoprostacyclin analogues of the formula (I) aredisclosed in U.S. Pat. No. 5,202,447 and Tetrahedron Lett. 31, 4493(1990). Furthermore, as described in U.S. Pat. No. 7,345,181, severalsynthetic methods are known to produce benzoprostacyclin analogues.

Known synthetic methods generally require one or more resolutions ofintermediates to obtain the pharmacologically active isomer of beraprostor a related benzoprostacyclin analogue. Also, current pharmaceuticalformulations of beraprost or a related benzoprostacyclin analogues mayconsist of several isomers of the pharmaceutical compound, and only oneof which is primarily responsible for the pharmacologic activity of thedrug. Isolation of the pharmaceutically active isomer of beraprostcompounds from current synthetic methods requires multiple preparativeHPLC or chromatographic purification procedures or multiplerecrystalizations that are not amenable to a commercially applicablescale. Therefore, it is desired to achieve an efficient, commerciallyapplicable synthetic route to the active isomer of beraprost or arelated benzoprostacyclin analogue.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method which canproduce the pharmaceutical compound represented by the general formula(I) in a substantially isomerically pure form, in fewer steps than theprior art and in commercially useful quantities. Another object of thepresent invention is to provide a method which can produce the tricyclicintermediates represented by the general formula (IV) and (V) in asubstantially isomerically pure form which can be used for theproduction of pharmaceutical compounds represented by the generalformula (I) or other similar compounds. Yet another object of thecurrent invention is to provide a novel method which can attach thealpha side-chain to single-isomer key intermediate leading to thepharmaceutical compound represented by the general formula (I). Thisinvention also claims the preparation of compound (VII) where 6, 2a=H,also referred to as the diol single-isomer exclusively in 95-100%purity, which can be transformed into beraprost and related derivativesof the general formula (I).

One embodiment provides for a process for preparing a compound of thefollowing formula:

wherein R¹ represents a cation, H, or C₁₋₁₂ alkyl, R² and R³ eachrepresent H or a hydroxy protective group, R⁴ represents H or C₁₋₃alkyl, and R⁵ represents H or C₁₋₆ alkyl, comprising the steps of:

-   (1) performing a cycloaddition reaction on the compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups, with a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above;

-   (2) aromatizing the cyclodiene of formula (IV) to form the aromatic    product of the following formula:

-   (3) Reducing the ester of the compound of formula (V) to a benzyl    alcohol and oxidation of benzyl alcohol to an aldehyde followed by    addition of a carbon to said aldehyde to form an alkyne resulting in    a compound of the following formula:

-   (4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)    represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to    its corresponding alkane to form a compound of the following    formula:

-   (5) selectively deprotecting the primary hydroxyl protective group,    followed by oxidation of the primary hydroxyl group to the    corresponding aldehyde, followed by coupling with a side-chain of    the formula:

wherein R⁴ and R⁵ are each defined above to form a compound of thefollowing formula:

-   (6) reduction of the ketone, deprotection of any remaining hydroxy    protective group and optionally converting the R^(1a) into a cation    or H to form a compound of the following formula.:

In another embodiment, the compound of formula (I) is produced as asubstantially pure single isomer. In another embodiment, R¹ is a cationor H, R² and R³ are H, R⁴ and R⁵ are CH₃. In another embodiment, R², R³,R^(2a) and R⁶ each independently represent trimethylsilyl,triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl,phenyldimethylsilyl, or tetrahydropyranyl. In another embodiment, thecycloaddition of step (1) is an inverse electron demand Diels Alderreaction followed by thermal decarboxylation. In another embodiment, thearomatization step (2) is treatment of the compound of formula (IV) withpalladium on carbon.

Another embodiment provides for a process of for preparing thestereoselectively produced isomeric compound of the following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups and R⁷ represents C₁₋₆alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl comprising the steps of:

-   (1) performing a cycloaddition reaction on the compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups to form a compound of the following formula:

wherein R^(2a), R⁶ and Ware each defined above;

-   (2) aromatization of the cyclodiene of formula (IV) to form the    aromatic product of the following formula:

wherein R^(2a), R⁶ and R⁷ are each defined above. In one embodiment,R^(2a) and R⁶ each independently represent trimethylsilyl,triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl,phenyldimethylsilyl, or tetrahydropyranyl. In another embodiment, thecycloaddition of step (1) is an inverse electron demand Diels Alderreaction followed by thermal decarboxylation. In another embodiment, thearomatization step (2) is treatment of the compound of formula (IV) withpalladium on carbon. Another embodiment provides a process for preparinga compound of the following formula:

wherein R^(1a) represents a cation, H, or C₁₋₁₂ alkyl, comprising thesteps of:

-   (1) performing a cycloaddition reaction on the compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups, with a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above;

-   (2) aromatizing the cyclodiene of formula (IV) to form the aromatic    product of the following formula:

-   (3) Reducing the ester of the compound of formula (V) to a benzyl    alcohol and oxidation of benzyl alcohol to an aldehyde followed by    addition of a carbon to said aldehyde to form an alkyne resulting in    a compound of the following formula:

-   (4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)    represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to    its corresponding alkane followed by deprotection of the hydroxyl    protective groups to form a compound of the following formula:

wherein R^(1a) represents a cation, H, or C₁₋₁₂ alkyl. In anotherembodiment, the compound of formula (VII) is produced as a substantiallypure single isomer.

Another embodiment provides for compounds represented by the formula:

wherein x is

R⁴ represents H or C₁₋₃ alkyl, andR⁵ represents H or C₁₋₆ alkyl, and the compound has a chiral purity ofat least 95%. Additional embodiments provide a chiral purity of at least95%, 97%, 99%, or greater than 99%. Another embodiment provides R⁴ andR⁵ are each CH₃.

Another embodiment provides for a process for preparing a substantiallypure compound of the following formula:

wherein

-   R² represents H or a hydroxy protective group,-   R⁴ represents H or C₁₋₃ alkyl,-   R⁵ represents H or C₁₋₆ alkyl, and-   Z represents C₁₋₁₂ alkyl-COOR¹², R¹² is a cation, H, or C₁₋₁₂ alkyl,    comprising the steps of:-   (1) reacting an aldehyde of the formula

with a substantially pure compound of the formula:

wherein Z′ is C₁₋₁₂ alkyl-COOR^(12′), R^(12′) is a C₁₋₆ alkyl or aprotecting group, R^(2a) is a hydroxy protecting group, R⁴ and R⁵ areeach defined above to form a compound of the following formula:

-   (2) selectively reducing the carbonyl and deprotecting secondary    alcohol to form a substantially pure compound of the following    formula:

and

-   (3) optionally deprotecting the ester of protected acid of Z′ to    form an acid or salt thereof. In one embodiment, the selective    reduction of the carbonyl includes an asymmetric catalyst. In one    embodiment, the step 3 is not optional, and Z′ is C₁₋₁₂    alkyl-COOR^(12′), and R^(12′) is a C₁₋₆ alkyl. In one embodiment,    the step 3 is not optional, and R⁴ and R⁵ are each CH₃, Z is    (CH₂)₃COOR¹² and R¹² is a cation or H. In one embodiment, R¹² is a    cation and the cation is K⁺. In one embodiment, the resulting    substantially pure compound comprises greater than 99% of the isomer    represented by the following formula:

DESCRIPTION OF THE FIGURES

FIG. 1 shows an embodiment of the synthesis of the side chain compoundfor coupling to the core beraprost analogue.

FIG. 2 shows Beraprost 314d and its isomers

FIG. 3 shows an embodiment of selective protection strategy leading toan enone intermediate

FIG. 4 shows an embodiment of the asymmetric synthesis of Beraprost froman enone intermediate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

All references cited herein are incorporated by reference in theirentirety.

Various inventions and/or their embodiments disclosed herein relate tomethods of synthesizing a substantially pure isomer of beraprost or itsrelated derivatives. In one preferred embodiment, the substantially pureisomer of beraprost is represented by the formula (I). In anotherpreferred embodiment, the substantially pure isomer of beraprost isBeraprost (314d) or a related analogue, such as a salt, solvate orprodrug thereof. Other embodiments include compounds that are novelintermediates of one or more of the synthetic routes disclosed herein.

wherein R¹ represents a cation, H, or C₁₋₁₂ alkyl, R² and R³ eachrepresent H or a hydroxy protective group, R⁴ represents H or C₁₋₃alkyl, and R⁵ represents H or C₁₋₆ alkyl.

Unless otherwise specified, “a” or “an” means “one or more” throughoutthis specification and claims.

The term “or” as used herein means “and/or” unless specified other wise.

Important synthetic methods which can be used as appropriate herein toprepare compounds are generally known in the art and are described in,for example, March's Advanced Organic Chemistry, 6^(th) Ed., 2007; T. W.Greene, Protective Groups in Organic Synthesis, John Wiley and Sons,1991.

When referring to a moiety (e.g. a compound) in singular, the plural ismeant to be included. Thus, when referring to a specific moiety, e.g.“compound”, this means “at least one” of that moiety, e.g. “at least onecompound”, unless specified otherwise.

As used herein, “halo” or “halogen” or even “halide” can refer tofluoro, chloro, bromo, and iodo.

As used herein, “alkyl” can refer to a straight-chain, branched, orcyclic saturated hydrocarbon group. Examples of alkyl groups includemethyl (Me), ethyl (Et), propyl (e.g., n-propyl and iso-propyl), butyl(e.g., n-butyl, iso-butyl, sec-butyl, tert-butyl), pentyl groups (e.g.,n-pentyl, iso-pentyl, neopentyl), and the like. In various embodiments,an alkyl group can have 1 to 30 carbon atoms, for example, 1-20 carbonatoms (i.e., C₁-C₂₀ alkyl group). In some embodiments, an alkyl groupcan have 1 to 6 carbon atoms, and can be referred to as a “lower alkylgroup.” Examples of lower alkyl groups include methyl, ethyl, propyl(e.g., n-propyl and iso-propyl), and butyl groups (e.g., n-butyl,iso-butyl, sec-butyl, tert-butyl). In some embodiments, alkyl groups canbe substituted as defined herein. In some embodiments, substituted,saturated hydrocarbons, C1-C6 mono- and di- and pre-halogen substitutedsaturated hydrocarbons and amino-substituted hydrocarbons are preferred,with perfluromethyl, perchloromethyl, perfluoro-tert-butyl, andperchloro-tert-butyl being the most preferred. The term “substitutedalkyl” means any unbranched or branched, substituted saturatedhydrocarbon, with unbranched C1-C6 alkyl secondary amines, substitutedC1-C6 secondary alkyl amines, and unbranched C1-C6 alkyl tertiary aminesbeing within the definition of “substituted alkyl,” but not preferred.In some embodiments, the term “alkyl” means any unbranched or branched,substituted saturated hydrocarbon. In some embodiments, cycliccompounds, both cyclic hydrocarbons and cyclic compounds havingheteroatoms, are within the meaning of “alkyl.” In some embodiments,“haloalkyl” can refer to an alkyl group having one or more halogensubstituents, and can be within the meaning of “alkyl.” At variousembodiments, a haloalkyl group can have 1 to 20 carbon atoms, forexample, 1 to 10 carbon atoms (i.e., C₁-C₁₀ haloalkyl group). Examplesof haloalkyl groups include CF₃, C₂F₅, CHF₂, CH₂F, CCl₃, CHCl₂, CH₂Cl,C₂Cl₅, and the like. Perhaloalkyl groups, i.e., alkyl groups where allof the hydrogen atoms are replaced with halogen atoms (e.g.,perfluoroalkyl groups such as CF₃ and C₂F₅), are included within thedefinition of “haloalkyl.” In some embodiments, “alkoxy” can refer to—O-alkyl group, and can be within the meaning of “alkyl.”. Examples ofalkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy(e.g., n-propoxy and isopropoxy), t-butoxy groups, and the like. Thealkyl group in the —O-alkyl group can be substituted with 1-5 R¹ groupsand R¹ is as defined herein.

As used herein, “hydroxy protective group” refers to the generallyunderstood definition of an alcohol or hydroxy protecting group asdefined in T. W. Greene, Protective Groups in Organic Synthesis, JohnWiley and Sons, 1991 (hereinafter “Greene, Protective Groups in OrganicSynthesis”).

As used herein, “protecting group” is used as known in the art and asdemonstrated in Greene, Protective Groups in Organic Synthesis.

As used herein, substantially pure compound or isomer refers to oneisomer being 90% of the resulting isomeric mixture, or preferably 95% ofthe resulting isomeric mixture, or more preferably 98% of the resultingisomeric mixture, or even more preferably 99% of the resulting isomericmixture, and most preferably above 99% of the resulting isomericmixture.

One aspect of the invention is a synthetic method for synthesizingBeraprost (314d) or a related analogue, such as a salt, solvate orprodrug thereof from a Corey Lactone, such as a compound represented byFormula (II) In one embodiment, the present invention relates to amethod for making a substantially pure isomer of beraprost or itsrelated derivatives of the following formula (I):

wherein R¹ represents a cation, H, or C₁₋₁₂ alkyl, R² and R³ eachrepresent H or a hydroxy protective group, R⁴ represents H or C₁₋₃alkyl, and R⁵ represents H or C₁₋₆ alkyl, comprising:

-   (1) performing a cycloaddition reaction between a compound of the    following formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups or H, and a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl, and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above;

-   (2) aromatizing the cyclodiene compound of formula (IV) to form the    aromatic product of the following formula:

-   (3) reducing the ester of the compound of formula (V) to a benzyl    alcohol and oxidation of benzyl alcohol to an aldehyde followed by    addition of a carbon to said aldehyde to form an alkyne resulting in    a compound of the following formula:

-   (4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)    represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to    its corresponding alkane to form a compound of the following    formula:

-   (5) selectively deprotecting the primary hydroxyl protective group,    followed by oxidation of the primary hydroxyl group to the    corresponding aldehyde, followed by coupling with a side-chain of    the formula:

wherein R⁴ and R⁵ are each defined above and (VIII) is substantially asingle isomer to form a compound of the following formula:

-   (6) reduction of the ketone, deprotection of any remaining hydroxy    protective group and optionally converting the R^(1a) into a cation    or H to form a compound of the following formula.:

In the present invention, the single pharmacologically active isomer ofberaprost corresponds to the 314-d isomer of beraprost or itscorresponding salt or other pharmaceutically useful related derivative,such as for example, prodrug or solvate. This 314-d isomer compound isrepresented by the compound of formula (I) wherein R¹ is a cation or H,R² and R³ are H, R⁴ and R⁵ are CH₃.

In one embodiment, R^(2a) and R⁶ independently represent hydroxyprotecting groups and are different protecting groups. In oneembodiment, R^(2a) is a silyl protecting group, such as for example,trimethylsilyl, triethylsilyl, t-butyldimethylsilyl,t-butyldiphenylsilyl, phenyldimethylsilyl. Additional silyl protectinggroups are recited in Greene, Protective Groups in Organic Synthesis,and are incorporated by reference. In one embodiment, R⁶ is a protectinggroup that is capable of protecting a primary alcohol without reactingwith a secondary alcohol, such as for example a trityl group. AdditionalR⁶ protecting groups meeting this requirement may be found in Greene,Protective Groups in Organic Synthesis, and are incorporated byreference.

In one embodiment, the cycloaddition of step (1) may be achieved with aninverse electron demand Diels Alder reaction followed by thermaldecarboxylation to form endo and exo isomers. The subsequentaromatization to compound (V) eliminates said isomers. In oneembodiment, aromatization may be achieved by dehydrogenation, forexample, palladium on carbon may be utilized to convert the diene ofcompound (IV) into the aromatic moiety of compound (V).

The reduction of the ketone in step (6) may be achieved using anon-selective reducing agent, such as for example, sodium borohydridewith cerium trichloride heptahydrate, and the subsequent diastereomersseparated, or alternatively a chiral reducing agent capable ofselectively reducing the ketone may be used to obtain substantially oneisomer of the resulting alcohol. Selective reducing agents are known inthe art and include, for example: (R)-(+)-2-Butyl-CBS-oxazaborolidineand catecholborane, (R)-(+)-2-Methyl-CBS-oxazaborolidine andcatecholborane, (+) DIP-chloride, NaBH₄ and2-(3-Nitrophenyl)-1,3,2-dioxaborolane-4S,5S-dicarboxylic acid(D-TarB-NO₂), modified DIBAL reagents, and modified LAH agents.

In one embodiment, the compound of formula (I) is produced as the singleisomer represented by formula (I) and in substantially isomerically pureform. In one embodiment, the product represented by formula (I)comprises 90% of the resulting isomeric mixture, or preferably 95% ofthe resulting isomeric mixture, or more preferably 98% of the resultingisomeric mixture, or even more preferably 99% of the resulting isomericmixture, and most preferably above 99% of the resulting isomericmixture.

In another embodiment of this invention is a method comprising steps (1)through (4) followed by deprotection of any alcohol protection groups toyield compound of formula (VII) wherein R^(2a) and R⁶ are H and R^(1a)is methoxy. This compound is isolated as substantially one isomerrepresented by the compound of formula (VII).

Another aspect of the present invention provides a novel method that canattach the alpha side-chain to single-isomer key intermediate leading tothe pharmaceutical compound represented by the general formula (I). Thenovel process provides for producing the four-carbon alpha side-chain ofberaprost or its related derivatives from the core intermediate ester ofthe compound of formula (V) comprising conversion of the compound offormula (V) to a benzyl alcohol of formula (X) followed by oxidation ofbenzyl alcohol to an aldehyde of formula (XII) followed by addition of acarbon to said aldehyde to form an alkyne compound of formula (VI). Oneskilled in the art would appreciate that extension of the alphaside-chain may proceed from the benzyl alcohol of formula (X) byconversion of the alcohol to a leaving group such as R¹⁰ of the formula(XI) followed by nucleophilic displacement. Furthermore, a Wittig orsimilar type reaction may be used to couple a side chain to the benzylaldehyde of formula (XII).

In another embodiment, analogues of the single-isomer key intermediatemay include an alpha side-chain of more than four carbons. For exampleScheme 1 demonstrates that the benzyl alcohol of formula (X) can beconverted to the compound of formula (XI) followed by nucleophilicdisplacement resulting in (XIII). In another embodiment, the aldehyde offormula (XII) may be subjected to a Wittig-type reaction to produce acompound of formula (XIII). In a further embodiment, the aldehyde offormula (VI) may be converted to a compound of formula (XIII) by methodsknown in the art or analogous to methods disclosed herein.

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups and R¹⁰ to R¹² are defined above, and may be optionallysubstituted with one or more functional groups. A compound of formula(XIII) can be subjected to steps (5) and (6) to produce additionalberaprost analogues.

Another aspect of this invention relates the side-chain coupling andvariations on said side-chain. the trans-alkene of beraprost and itsderivatives is achieved through Wadworth-Emmons-type reaction. Theside-chain is produced as substantially a single isomer. Synthesis ofthe side-chain coupling product of the formula (VIII) may be achievedfrom a single isomer Weinreb amide compound of the following formula:

wherein R⁴ and R⁵ are each defined above.

Furthermore, the compound of formula (XIV) may be synthesized accordingto reagents known in the art from a compound of the formula (XV) bydeprotonation and subsequent selective addition to an compound with asuitable leaving group, such as for example compound (XVI).

resulting in the compound:

The compound of formula (XVII) may be converted to a compound of formula(XIV) by methods known in the art. Compound (XIV) may subsequently beconverted in to a compound of the formula (VIII) by methods analogous tothose disclosed herein.

Furthermore, another embodiment of this invention includes manipulationof the side chain coupling product as shown in Scheme 2. Variation ofthe side-chain allows additional analogues of beraprost to be explored.In one embodiment, the compound of the formula (XV) may be reacted witha compound of the formula (XVIII), wherein R¹³ is C₁₋₁₂ allyl, C₁₋₁₂alkene, C₁₋₁₂ alkyne, C₁₋₁₂ cyclo alkyl, C₁₋₁₂ cyclo alkene, or C₁₋₁₂cyclo alkyne, and further manipulated by methods analogous to thosedisclosed herein or known in the art to form a Weinreb amide of formula(XIX). The methods for these reactions are analogous to those for theproduction of compound (XIV) or are known in the art. A compound of theformula (XIX) may then be converted into a coupling product suitable forWadworth-Emmons-type coupling analogous to compound of formula (VIII).The resulting coupling product may be coupled with a compound suitablefor Wadworth-Emmons-type coupling disclosed herein, for example acompound of the formula (VII) that has been selectively deprotected atthe primary hydroxyl protective group, followed by oxidation of theprimary hydroxyl group to the corresponding aldehyde.

wherein R⁴ and R¹³ are previously defined. In one embodiment, X is H. Inanother embodiment, X is Ph. Additional moieties, such as analogues ofPh and other aryl, heteroaryl or alkyl moieties may also serve as X. Inone embodiment, the phosphonate product is produced with chiral purityof 97 percent or more, or 99 percent or more. Additional embodimentsinclude side-chain compounds represented by the structures

wherein R⁴, R⁵ and R¹³ are previously defined and the chiral purity is97 percent or more, or 99 percent or more. A preferred embodimentincludes compounds represented by the structures

wherein the chiral purity is 97 percent or more, or 99 percent or more.

Side-chain compounds may be produced by the methods described herein,including the exemplary methods shown in FIG. 1

The present invention is further illustrated by, though in no waylimited to, the following examples.

Example 1 Synthetic Route to the Single Isomer of a Compound of Formula(I)

Preparation of (2) A 1-L, three-necked, round-bottomed flask equippedwith a mechanical stirrer, a dropping funnel, a thermocouple and anargon inlet-outlet adapter connected to a bubbler was charged with Coreylactone (1) (10 g), anhydrous dichloromethane (100 mL), and 2,6-lutidine(27 mL) under argon. A solution of t-butyldimethyl trifluoromethanesulfonate (37.4 mL) in dichloromethane (50 mL) was added to the reactionmixture drop-wise, while keeping the temperature between −10° C. to −20°C. over a period of 20-40 minutes. After complete addition, the reactionmixture was allowed to warm-up to ambient temperature. After 2-4 h, theprogress of the reaction was monitored by thin-layer chromatography.After completion of the reaction, the reaction mixture was concentratedin vacuo to obtain a crude product. The crude product was chased withMTBE to remove dichloromethane completely. The crude product wasdissolved in MTBE (100-150 mL) and washed with water (1×100 mL),saturated sodium bicarbonate (1×100 mL), brine (1×150 mL), dried overanhydrous sodium sulfate (10 g), and filtered. The filtrate wasevaporated in vacuo to a afford crude, viscous liquid (30.4 g). Thecrude product was purified by column chromatography using 230-400 meshsilica gel. A solvent gradient of ethyl acetate in hexanes (2-12%) wasused to elute the product from the column. All fractions containing thedesired product were combined and concentrated in vacuo to give pureproduct (2) as a white solid (20.8 g, 89.4%).

Preparation of (3) A 1-L, two-necked, round-bottomed flask equipped witha mechanical stirrer, a dropping funnel, a thermocouple and an argoninlet-outlet adapter connected to a bubbler was charged withintermediate 2 (20.0 g), and toluene (200 mL). The temperature of thereaction mixture was maintained at −50° C. to −70° C. under nitrogenusing dry-ice-acetone bath. While maintaining the temperature of thereaction mixture at −50° C. to −70° C., diisobutylaluminium hydride(DIBAL, 60 mL, 1.0M in toluene) was added drop wise during 20-30minutes. The progress of the reaction was monitored by TLC. The reactionmixture was quenched with methanol (10 mL) at −20° C., water (300 mL),followed by addition of diluted hydrochloric acid (˜20%). The organiclayer was separated and aqueous layer was extracted with MTBE (2×100mL). The combined organic layers were washed with saturated sodiumbicarbonate (1×150 mL), brine (1×150 mL) and, dried over sodium sulfate(10 g). The organic layer was filtered. The filtrate was concentrated invacuo, to give a yellow, viscous oil (20.4 g). The crude product wasused as such in the next step.

Preparation of (4) A 1-L, three-necked, round-bottomed flask equippedwith a mechanical stirrer, a thermocouple, and an argon inlet-outlettrap was charged with lactol intermediate 3 (20 g), anhydrousdichloromethane (200-250 mL), triethylamine (69.2 mL), and dimethylaminopyridine (DMAP, 0.6 g). The temperature of the reaction mixture wasreduced to −20° C. A solution of methanesulfonyl chloride (7.7 mL) wasadded drop wise under argon while keeping the temperature around −20° C.After complete addition, the progress of the reaction was monitored byTLC. The temperature of the reaction mixture was allowed to warm-up toambient temperature. The reaction mixture was heated to reflux for 2-4h. The reaction mixture was concentrated in vacuo to obtain crudeproduct. The crude product was purified by column chromatography using230-400 mesh silica gel and eluted with a gradient solvent of ethylacetate in hexanes (0-10%). The fractions containing the desired productwere combined and evaporated in vacuo to afford intermediate 4 (as aviscous liquid, 11 g).

Preparation of (6) A 1-L, two-necked, round-bottomed flask equipped witha mechanical stirrer, and an argon inlet-outlet trap was charged with asolution of intermediate (4, 10.0 g), dichloroethane (DCE, 100-150 mL),compound 5 (2.6 g), and Eu(hfc)₃ (1.4 g) at room temperature underargon. The reaction mixture was stirred and heated to reflux for 1.0 hand the progress of the reaction was monitored by TLC in order to ensurethat starting material 5 has been consumed completely. After 1.0 h, thetemperature of the reaction was reduced below reflux temperature andcompound 5 (1.0 g) was added to the reaction mixture. The temperature ofthe reaction was increased to reflux. In a similar manner, after half anhour, compound 5 (0.9 g) was added and the reaction was continuouslyrefluxed again. When the TLC of the reaction mixture indicated almostcomplete consumption of intermediate 4, the solvent was evaporated undervacuum to give a residual viscous liquid. The brown, viscous liquid waschased with toluene and dissolved in toluene (100-150 mL). The reactionmixture was heated to reflux again for 6-8 h. The progress of thereaction was monitored by TLC. After completion of the reaction, it wasconcentrated in vacuo to obtain the crude product 6 as a viscous oil.The crude product was purified by column chromatography using 230-400mesh silica gel and eluted with a gradient solvent of ethyl acetate inhexanes (4-40%). The fractions containing the desired product werecombined and concentrated in-vacuo to yield the intermediate 6, as acolorless, viscous oil (9.87 g, 77%).

Preparation of (7) A 500-mL, one-necked, round-bottomed flask equippedwith a magnetic stirrer, an argon inlet-outlet trap, and a condenser wascharged with a solution of intermediate 6 (7.6 g) in toluene (70-100 mL)under argon. At room temperature, palladium on carbon (1.52 g, 5%, 50%wet) was charged, and the reaction mixture was heated to reflux for 8-12h. The reaction mixture was allowed to cool to room temperature, and thereaction mixture was filtered through a pad of Celite. The filtrate wasconcentrated in-vacuo to yield crude product 7, as a viscous liquid. Thecrude product 7 was purified by column chromatography using 230-400 meshsilica gel. A solvent gradient of ethyl acetate in hexanes (0-15%) wasused to elute the product from the column. The fractions containing thedesired product were evaporated in-vacuo to yield pure key intermediate(7) as viscous liquid (4.0 g, 43%).

Preparation of (8) A 500-mL, three-necked, round-bottomed flask equippedwith a magnetic stirrer, and an argon inlet-outlet trap, and athermocouple was charged with a solution of intermediate 7 (3.90 g) intoluene (40-60 mL, anhydrous). The reaction mixture was cooled to −25°C. to −50° C., and diisobutylaluminium hydride solution (DIBAL, 16.60mL, 1.0M in toluene) was added drop-wise, while keeping the temperatureof the reaction mixture between −25° C. to −50° C. The reaction mixturewas stirred for 1-2 h. The progress of the reaction was monitored byTLC. The reaction mixture was quenched with methanol (2-4 mL), followedby acidification with dilute hydrochloric acid (20%, 50 mL). The organiclayer was separated and aqueous layer was extracted with MTBE (2×50 mL).The combined organic layers were washed with saturated sodiumbicarbonate (1×50 mL), brine (1×50 mL), and dried over sodium sulfate(10 g). The organic layer was filtered. The filtrate was concentrated invacuo, to give a viscous oil (8, 3.73 g).

The crude product 8 was used as such in next step.

Preparation of (9) A 500-mL, one-necked, round-bottomed flask equippedwith a magnetic stirrer was charged with a solution of intermediate 8 indichloromethane (40-70 mL), and manganese dioxide (8.30 g) undernitrogen. The reaction mixture was stirred vigorously at ambienttemperature over night. The progress of the reaction was monitored byTLC. The reaction mixture was filtered through a pad of Celite and thefiltrate was concentrated in-vacuo to obtain the crude product 9 ascolorless, viscous liquid oil (3.4 g, 92%). In this case the crudeproduct was used as such in the next step (as the TLC indicated purematerial). The crude product 9 may optionally be purified by columnchromatography.

Preparation of (10) A 50-mL, one-necked, round-bottomed flask equippedwith a magnetic stirrer, and an argon inlet-outlet trap was charged witha solution of intermediate 9 (260 mg) in methanol (5-10 mL), potassiumcarbonate (232 mg), and dimethyl(1-diazo-2-oxopropyl)phosphonate (215mg) at room temperature under argon. The mixture was stirred at ambienttemperature over night. After ˜16 h, the progress of the reaction wasmonitored by TLC. The solvent was evaporated in vacuo and dissolved inMTBE (10-15 mL). The organic layer was washed with brine (1×10 mL),dried over anhydrous sodium sulfate, filtered, and the filtrateconcentrated in vacuo to obtain crude product 10, as a viscous oil.

Preparation of (11) A 50-mL, one-necked, round-bottomed flask equippedwith a magnetic stirrer, and an argon inlet-outlet trap was charged witha solution of intermediate 10 (55 mg) in acetonitrile (5-10 mL), andcopper iodide (3 mg) at room temperature under nitrogen. To the stirredsolution, ethyl diazoacetate (14 mg dissolved in 1.0 mL of acetonitrile)was added. The reaction mixture was stirred overnight. The progress ofthe reaction was monitored by TLC. The reaction mixture was concentratedin-vacuo to give the crude product 11. The crude product was purified bycolumn chromatography using 230-400 mesh silica gel and the column waseluted with a gradient solvent of ethyl acetate in hexanes (0-10%). Thefractions containing the desired compound were evaporated in vacuo toyield intermediate 11, as a colorless, viscous oil (38 mg, 60%).

Preparation of (12) A 50-mL, three-necked, round-bottomed flask equippedwith magnetic stirrer was charged with a solution of intermediate 11 (50mg) in anhydrous acetonitrile (5-10 mL) and palladium on carbon (10 mg,5%, wet 50%). The reaction mixture was stirred and air was removed byvacuum. The vacuum in the flask was replaced by hydrogen from anattached balloon. The process was repeated 5-10 times. Finally, thereaction mixture was stirred at room temperature under hydrogenovernight. The progress of the reaction was monitored by TLC. Aftercompletion of the reaction, the reaction mixture was filtered through apad of Celite and the filtrate concentrated in-vacuo to give the crudeproduct 12. The crude product 12 was purified by flash columnchromatography using 230-400 mesh silica gel. A solvent gradient ofethyl acetate in hexanes (2-8%) was used to elute the product from thecolumn. The fractions containing the desired product 12 were combinedand evaporated in-vacuo to yield product 12, 41 mg (˜80%).

Preparation of (13) A 25-mL, one-neck, round-bottomed flask equippedwith a magnetic stirrer was charged with intermediate 12 in a solutionof acetic acid: THF: water (1.0:3.0:0.5). The reaction mixture wasstirred at ambient temperature overnight. The progress of the reactionwas monitored by TLC. After approximately 90% completion of the reaction(by TLC), the reaction mixture was concentrated in-vacuo to give aresidual viscous liquid. The crude product was dissolved in ethylacetate (10 mL) and organic layer was washed with saturated sodiumbicarbonate solution (1×10 mL), brine (1×10 mL), dried over anhydroussodium sulfate (1.0 g), filtered and the filtrate evaporated in-vacuo.The crude product 13 was purified by column chromatography using 230-400mesh silica gel. A solvent gradient of ethyl acetate in hexanes (4-100%)was used to elute the products from the column. The fractions containingthe desired product 13 were combined and evaporated in-vacuo to yield aviscous liquid of pure product 13, (120 mg). The purification of crudeproduct by column also gave starting material 12 (36 mg), diol product(52 mg).

Preparation of (14) A 100-mL, one-neck, round-bottomed flask equippedwith a magnetic stirrer, an argon inlet-outlet trap was charged with asolution of intermediate 13 (160 mg) in dichloromethane (5-10 mL). Tothe stirred solution, add Dess-Martin reagent (233 mg) at ambienttemperature under nitrogen. The reaction mixture was stirred for 0.5-1.0h. The progress of the reaction was monitored by TLC. The reactionmixture was quenched with NaHCO₃ (solid powder, 500 mg). The product 14was purified by column chromatography using 230-400 mesh silica gel byloading the reaction mixture directly on the column, and the column waseluted with dichloromethane (100%). The fractions containing the desiredproduct 14 were evaporated in-vacuo to yield pure product 14 (125 mg,73%).

Preparation of (15) A 50-mL, three-neck, round-bottomed flask equippedwith a magnetic stirrer and an argon inlet-outlet trap was charged withthe phosphonate side-chain (57 mg), THF (5 mL), and sodium hydride (9.0mg). The mixture was stirred at 0-10° C. for 15-20 minutes undernitrogen. The intermediate 14 (85 mg, dissolved in 5 mL of THF) wasadded drop-wise during a period of 5-10 minutes. The reaction mixturewas stirred 2-3 h. The temperature of the reaction mixture was allowedto rise to ambient temperature. The progress of the reaction wasmonitored by TLC after 2-3 h. The reaction mixture was quenched withacetic acid (couple of drops) and the reaction mixture was extractedwith MTBE (3×10 mL). The combined organic layers were washed withsaturated sodium bicarbonate (1×10 mL), brine (1×10 mL), dried overanhydrous sodium sulfate, filtered, and evaporated in-vacuo to give acrude product. The crude product 15 was purified by columnchromatography using 230-400 mesh silica gel, the column was eluted withgradient of ethyl acetate and hexanes (5-12%). The pure fractionscontaining the desired compound 15 were combined and evaporated in-vacuoto yield pure product 15 as a viscous liquid (72 mg, 70%).

Preparation of (16) A 50-mL, one-neck, round-bottomed flask equippedwith a magnetic stirrer, was charged with a solution of intermediate 15in methanol and cerium chloride heptahydrate (CeCl₃.7H₂O, 28 mg). To thereaction mixture, sodium borohydride (1.74 mg) was added and thereaction mixture was stirred at temperature 0-10° C. for 1-2 h. Theprogress of the reaction was monitored by TLC. The reaction mixture wasquenched with acetic acid (0.2 mL), saturated solution of ammoniumchloride (2 mL) and brine (10 mL). The reaction mixture was extractedwith ethyl acetate (3×15 mL). The combined organic layers were washedwith brine, dried over anhydrous sodium sulfate, filtered, andevaporated in-vacuo to give crude product 16 (46 mg). The crude productwas used as such in the next step.

Preparation of (17) A 50-mL, one-neck, round-bottomed flask equippedwith a magnetic stirrer, was charged with a solution of intermediate 16in methanol and hydrochloric acid (a few drops). The reaction mixturewas stirred at ambient temperature for 1-2 h. The progress of thereaction was monitored by TLC. The reaction mixture was quenched with asolution of saturated sodium bicarbonate, then brine (10 mL) andextracted with ethyl acetate (3×10 mL). The combined organic layers werewashed with brine (1×10 mL), and dried over anhydrous sodium sulfate (1g), filtered, and the filtrate was evaporated in-vacuo to give crudeproduct. The crude product was purified by column chromatography using230-400 mesh silica gel and eluted with ethyl acetate in hexanes(10-70%). The fractions containing the desired product (lower spot onTLC) were evaporated in-vacuo to yield pure product 17 (22 mg, ˜50% overtwo steps, one isomer only).

Preparation of (18) A 50-mL, one-neck, round-bottomed flask equippedwith a magnetic stirrer, was charged with a solution of intermediate 17in methanol and the solution of sodium hydroxide (15 mg in 1.0 mL ofwater). The reaction mixture was stirred at ambient temperatureovernight. The progress of the reaction was monitored by TLC. Additionalamount of sodium hydroxide (25 mg dissolved in 1.0 mL of water) wasadded and temperature of the reaction mixture was raised to 45° C.-55°C. for 6-8 h. The progress of the reaction was monitored by TLC. Thesolvent was evaporated in-vacuo to remove methanol, and water was addedto the reaction mixture. The aqueous layer was extracted withdichloromethane (3×10 mL) to remove impurities. The pH of the aqueouslayer was adjusted to 2-3 by addition of dilute hydrochloric acid andthe aqueous layer was extracted with ethyl acetate (3×10 mL). Thecombined organic layers were washed with water (1×10 mL), brine (1×10mL), and dried over anhydrous sodium sulfate (1 g), filtered, and thefiltrate was evaporated in-vacuo to give crude product (314-d isomer ofberaprost, 18 mg).

Preparation of (19) A 50-mL, one-neck, round-bottomed flask equippedwith a magnetic stirrer, was charged with a solution of free 314-disomer of beraprost (18) in methanol and the solution of sodiumhydroxide (2 mg dissolved in 1.0 mL of water). The reaction mixture wasstirred at ambient temperature for 1-2 h. The solvent was evaporatedin-vacuo to remove methanol and water. Toluene (5 mL) was added to theresidual, yellow, and viscous material and the toluene was removedin-vacuo to give the solid sodium salt 314-d isomer of beraprost (21mg). A chiral HPLC assay indicated 314-d isomer of beraprost (84%) andit was confirmed by comparing with references of 314-d isomer ofberaprost (one reference consists of 314-d isomer of beraprost and otherreference consists of mixture of four isomers including 314-d isomer ofberaprost).

Example 2 Side-Chain Formation

Preparation of (21) The benzyl-substituted oxazolidinone 20 was selectedas the starting material. It had given a high selectivity in thesynthesis. Deprotonation of 20 with NaN(SiMe₃)₂ and treatment of thecorresponding sodium enolate with freshly prepared 1-iodo-2-butyne,which was prepared from the commercially available 1-bromo-2-butyne,gave the substituted oxazolidinone 21 in 70-90% yield. Reaction ofoxazolidinone 21 with 1-bromo-2-butyne never went to completion, evenwith excess of reagent. 1-iodo-2-butyne can be prepared from2-butyn-1-ol or 1-bromo-2-butyne, whereas the in-situ preparation of1-iodo-2-butyne from 1-bromo-2-butyne is more convenient and preferable.

Preparation of (22) To a 250 mL, three-necked, round-bottomed flaskequipped with a mechanical stirrer and an argon inlet-outlet adapterconnected to a bubbler was charged with a solution of oxazolidinone 21(8.095 g) in EtOH (100 mL), followed by addition of Ti(OEt)4 (6.473).The mixture was heated to reflux for 7-10 h. The reaction mixture wasconcentrated in a rotary evaporator at 20° C./50 mbar. The residue wasdissolved in EtOAc (100 mL) and concentrated the rotary evaporator, andthe crude material was adsorbed on silica gel and purified by columnchromatography (gradient: ethyl acetate/hexanes, 2-6%) to give ester 22(6.27 g).

Preparation of (23) To a 250 mL, three-necked, round-bottomed flaskequipped with a mechanical stirrer and an argon inlet-outlet adapterconnected to a bubbler was charged with a solution of ester 22 (6.0 g)and [MeO(Me)NH₂]Cl (9.5 g) in THF (75 mL). To the solution was addeddrop-wise i-PrMgCl (48.6 mL, 2.0 M in THF) at 20° C. during 45 min by adropping funnel. After the mixture was stirred at 20° C. for 30 min,aqueous NH₄Cl (4 mL) was added. The mixture was allowed to warm toambient temperature and diluted with MTBE (25 mL). The suspension wasfiltered through a pad of Celite and concentrated in vacuo. The crudeproduct was purified by column chromatography (gradient: EtOAc/hexanes,5-25%) to afford Weinreb amide 23 (3.45 g, 73% over two steps) as acolorless oil.

Preparation of (24) To a 250 mL, three-necked, round-bottomed flaskequipped with a mechanical stirrer and an argon inlet-outlet adapterconnected to a bubbler was charged with a solution of Dimethylmethylphosphonate (5.279 g) in THF (30 mL), followed by drop-wiseaddition of n-BuLi (22.16 mL of 1.6 M in hexanes) at 78° C. by adropping funnel. The mixture was stirred at 78° C. for 1 h and then asolution of amide 23 (3.00 g) in THF (20 mL) was added during 30-45minutes via the dropping funnel. After the mixture was stirred at 78° C.for 2 h, aqueous NH₄Cl (4 mL) was added. The reaction mixture wasallowed to warm to ambient temperature, diluted with MTBE (50 mL),filtered and concentrated in vacuo. The crude product was purificationby column chromatography (gradient, EtOAc/hexanes, 0-8%) to affordphosphonate 24 (3.799 g, 92%).

Example 3 Preparation of Enone Intermediate from Ester Diol

Step 1: Protection of the Primary Alcohol

A 500 mL, two-necked, round-bottom flask equipped with a magnetic stirbar and an argon inlet-outlet adapter was charged with a solution ofester diol (1) (10.00 g) in dichloromethane (200 mL). To this solutiontriethylamine (13.21 g), 4-(dimethylamino)pyridine (4.0 g), and DMF (20mL) were added at ambient temperature under argon. The mixture wasstirred until a clear solution was obtained. The reaction was stirredfor ˜31 h at ambient temperature. After ˜31 h, the progress of thereaction was monitored by TLC. The mixture was washed with saturatedammonium chloride (200 mL). The organic layer was separated, dried overanhydrous sodium sulfate, filtered, and concentrated in vacuo to givethe crude product (2) as a viscous oil. The crude product from another10-g batch was combined and purified by column chromatography using230-400 mesh silica gel and eluted with a gradient solvent of ethylacetate in hexanes (5-50%). The fractions containing the desiredcompound (by TLC) were evaporated in vacuo to yield trityl ether (2)(33.82 g, 94.6% from two 10-g batches). The compound was characterizedby spectral data.

Step 2: Protection of the Secondary Alcohol

A 1000 mL, two-necked, round-bottom flask equipped with a magnetic stirbar and an argon inlet-outlet adapter was charged with a solution oftrityl ether (2) (39.50 g) in anhydrous dichloromethane (600 mL). Tothis solution, 2,6-lutidine (18.51 g) was added at ambient temperatureunder argon. The mixture was stirred until a clear solution wasobtained. The mixture was cooled to −15° C. and TBDMS triflate (22.84 g)was added in portions while maintaining the temperature below −10° C.The reaction was stirred for ˜1 h and the progress of the reaction wasmonitored by TLC. At this stage the reaction was complete. To thereaction mixture hexanes were added (600 mL) and temperature was allowedto rise to ambient. This mixture was passed through a pad of 230-400mesh silica gel (384 g) and eluted with a gradient solvent of ethylacetate in hexanes (5-15%). The fractions containing the desiredcompound were evaporated in vacuo to yield silyl ether (3) (47.70 g,99.6%). The compound was characterized by spectral data.

Step 3: Deprotection of the Primary Alcohol

A 500 mL, two-necked, round-bottom flask equipped with a magnetic stirbar and an argon inlet-outlet adapter was charged with a solution oftrityloxy-TBDMS ether (3) (14.58 g) in anhydrous dichloromethane (175mL). To this solution, diethylaluminum chloride (22.00 mL, 1M indichloromethane, 1.0 eq.) was added at ambient temperature under argon.The reaction was stirred for −3 h and the progress of the reaction wasmonitored by TLC. At this stage reaction was not complete and an extraone equivalent of diethylaluminum chloride (22.00 L, 1M indichloromethane, 1.0 eq.) was added at ambient temperature, and thereaction mixture was stirred for another 3 h while the progress wasmonitored by TLC. After a total of 6 h the reaction mixture showed thepresence of some starting material and another 0.5 equivalent of diethylaluminum chloride (11.00 mL, 1M in heptane, 0.5 eq.) was added atambient temperature and reaction mixture was stirred for another I h andprogress of the reaction was monitored by TLC. At this stage reactionwas complete, and the reaction mixture was cooled to 0° C. To thereaction mixture, saturated sodium bicarbonate solution (240 mL) wasadded (Note 2). Once the temperature raised to ambient, and the compoundwas extracted with dichloromethane. The combined extracts ofdichloromethane were washed with brine, dried over sodium sulfate andevaporated in vacuo to obtain a crude, viscous oil (14.01 g). This crudecompound was passed through a pad of 230-400 mesh silica gel (197 g) andeluted with a gradient solvent mixture of ethyl acetate in hexanes(10-50%). The fractions containing the desired compound were evaporatedin vacuo to yield hydroxy-silyl ether (4) (8.54 g, 92.3%). The compoundwas characterized by spectral data.

Step 4: Oxidation of Primary Alcohol and Coupling Resulting in EnoneIntermediate

To a cooled (−78° C.) and stirred solution of oxalyl chloride (23.00 mL)in dichloromethane (60 mL) was added slowly a solution of dimethylsulfoxide (4.33 mL) in dichloromethane (35 mL) under argon. Afterstirring for 45 minutes at −78° C. to −70° C., a solution of alcohol (4)(8.54 g) in dichloromethane (60 mL) was added to this reaction mixturewhile maintaining the temperature below −65° C. After stirring for 60minutes at −65° C., temperature of reaction mixture was raised to −45°C. to −40° C. and stirred for 60 minutes at this temperature. Thisreaction mixture was cooled to −65° C. and quenched by slow addition oftriethylamine (14.15 mL) (Note 1). The reaction mixture was stirred foranother 30 minutes at −65° C. and the completion of reaction was checkedby the TLC. The temperature of reaction mixture was raised to ambientand water (60 mL) was added. The two-phase mixture was stirred for 5minutes at room temperature after which the organic phase was separatedand the aqueous phase was extracted with dichloromethane (2×75 mL) toensure complete extraction of product into the organic layer. Thecombined organic extracts were washed with brine (100 mL), dried oversodium sulfate and evaporated in vacuo to obtain crude aldehyde (9.77g). In a separate 500-mL, two-necked, round-bottom flask equipped with amagnetic stir bar and an argon inlet-outlet adapter, a solution ofphosphonate side chain (8.50 g) in MTBE (175 mL) was charged. To thisLiOH.H₂O (1.86 g) was added and the mixture was stirred for −1 h. After−1 h, a solution of crude aldehyde (5) in MTBE (175 mL) was added slowlyover a period of 10 minutes and stirred until completion of reaction(Note 3). Progress of reaction was monitored by TLC (Note 3). After thereaction was complete, the reaction mixture was quenched by adding water(175 mL) and the mixture stirred for 15 minutes. The organic layer wasseparated and aqueous layer was extracted with ethyl acetate (3×70 mL).The combined organic extracts were washed with water (70 mL), brine (30mL), dried over sodium sulfate and evaporated in vacuo to obtain acrude, viscous liquid of enone intermediate (6) (11.22 g). This crudeenone intermediate (6) was passed through a pad of 230-400 mesh silicagel (328 g) and eluted with a gradient solvent of ethyl acetate inhexanes (2-20%). The fractions containing the desired compound wereevaporated in vacuo to yield enone (6) (19.42 g, 80%; This crudecompound was combined with 14.99 g of crude compound from another lotand a combined column chromatography was performed on two lots). Thepure compound was characterized by spectral data.

Example 4 Preparation of Compound (A)

Option 1: Reduction/Deprotection

Step 1: Selective Reduction

A 100 mL, three-necked, round-bottom flask equipped with a magnetic stirbar, a thermocouple, and an argon inlet-outlet adapter was charged withenone compound (0.11 g) and anhydrous toluene (5.0 mL). A solution of(R)-(+)-2-methyl CBS oxazaborolidine (1.0 M in toluene) (0.43 mL) wasadded under argon at ambient temperature. The mixture was cooled to ˜O°C. (dry ice/acetone-bath), and borane-methyl sulfide complex (0.32 mL)was added slowly maintaining the temperature between −40° C. and −30° C.After complete addition, the reaction mixture was stirred for 1-2 h at−30° C. to −25° C. The progress of the reaction was monitored by TLC.The reaction mixture was carefully quenched by slow addition of methanol(2.0 mL) over a period of 2-3 minute maintaining the temperature between−15° C. and −10° C. The reaction mixture was allowed to warm to roomtemperature and the stirring was continued for another 20-30 minutes. Atthis stage, saturated aqueous ammonium chloride solution (5.0 ml) wasadded with stirring. The organic layer was separated, and the aqueouslayer was extracted with ethyl acetate (2×15 mL). The combined organiclayers were washed with brine (10 mL), dried over anhydrous sodiumsulfate, filtered and concentrated in vacuo to give crude alcohol (A)(0.27 g). This crude alcohol (A) was passed through a pad of 230-400mesh silica gel (22.5 g) and eluted with a gradient solvent of ethylacetate in hexanes (0-12%). The fractions containing the desiredcompound were evaporated in vacuo to yield pure alcohol (7) (0.096 g,87.2%). The compound was characterized by spectral data.

Step 2: Deprotection of Protected Alcohol

To a solution of TBDMS protected ether (2.67 g) in methanol (50 mL) wasadded 10% aqueous HCl 10.00 mL) at room temperature. The reactionmixture was stirred at ambient temperature until completion of reaction.After −1 h the reaction mixture was checked by TLC for its completion.At this stage, the reaction mixture was neutralized with saturatedsodium bicarbonate 10 mL) to pH 7-8 and concentrated in vacuo to removemethanol. The reaction mixture was diluted with water 10 mL) and themixture was then extracted with ethyl acetate (3×30 mL). The combinedethyl acetate extracts were washed with brine (15 mL), dried (Na₂SO₄),filtered and concentrated in vacuo to give beraprost ester (A) as acrude, pale-yellow, viscous liquid (2.31 g). The crude product waspurified by column chromatography using a gradient solvent of ethylacetate in hexanes (0-90%). The fractions containing the desiredcompound were evaporated in vacuo to yield beraprost ester (A) (1.26 g)which was crystallized using a ethyl acetate and cyclopentane mixture toobtain ester with a chiral purity of 96.24% (by HPLC); mp 82-83° C.(dec.); Required: C=72.79; H=7.82; Found C=72.86; H=7.41. The compoundwas characterized by spectral data.

Option 2: Deprotection/Reduction

Step 1: Deprotection of Protected Alcohol

To a solution of enone (0.450 g) in methanol (10 mL) was added 10%aqueous HCl (0.90 mL) at ambient temperature. The reaction mixture wasstirred at ambient temperature until completion of reaction. After −3 hthe reaction mixture was checked by TLC for its completion. At thisstage, the reaction mixture was neutralized with saturated sodiumbicarbonate to pH 7-8 and concentrated in vacuo to remove methanol. Thereaction mass was diluted with water (10 mL) and the mixture wasextracted with ethyl acetate (2×15 mL). The combined ethyl acetateextracts were washed with brine (10 mL), dried (Na₂SO₄), filtered andconcentrated in vacuo to give the keto alcohol as a crude, pale-yellow,viscous liquid (0.400 g). The crude product was crystallized using aethyl acetate and hexanes mixture to obtain pure, crystallineketo-alcohol (0.210 g, 60%); mp 75-76° C.; The compound wascharacterized by spectral data.

Step 2: Selective Reduction

A 100 mL, three-necked, round-bottom flask equipped with a magnetic stirbar, a thermocouple, and an argon inlet-outlet adapter was charged withketo-alcohol (8) (3.25 g) and anhydrous toluene (100 mL). A solution of(R)-(+)-2-butyl CBS oxazaborolidine (1.0 M in toluene) (23.8 mL) wasadded under argon at room temperature. The mixture was cooled to −15° C.(dry ice/acetone-bath), and catecholborane (23.8 mL) was added slowlymaintaining the temperature between −15° C. and −10° C. After completeaddition, the reaction mixture was stirred for 1-2 h while slowlyallowing the temperature to raise to ambient temperature. The progressof the reaction was monitored by TLC. The reaction mixture was carefullyquenched by slow addition of methanol (50 mL) over a period of 10minutes maintaining the temperature between −15° C. and −10° C. Thereaction mixture was allowed to warm to room temperature and thestirring was continued for another 20-30 minutes. At this stage,saturated aqueous ammonium chloride solution (10 ml) was added withstirring. The organic layer was separated, and the aqueous layer wasextracted with ethyl acetate (3×50 mL). The combined organic layers werewashed with brine (15 mL), dried over anhydrous sodium sulfate, filteredand concentrated in vacuo to give crude beraprost ester (A). The crudeproduct was purified by column chromatography using a gradient solventof ethyl acetate in hexanes (0-90%). The fractions containing thedesired compound were evaporated in vacuo to yield beraprost ester (A)(2.53 g, 77%). A small sample was crystallized using an ethyl acetateand hexanes mixture to obtain analytically pure beraprost ester diol mp75-76° C. The compound was characterized by spectral data.

Example 5 Compound A to Beraprost 314d to a Salt

Synthesis of Beraprost 314d

To a solution of beraprost ester (A) (0.700 g) in methanol (10 mL) wasadded a solution of sodium hydroxide (0.815 g in 2.0 mL water) at roomtemperature. The reaction mixture was stirred at room temperature for−16 h and the progress of the reaction was monitored by TLC. Thereaction mixture was concentrated in vacuo to remove methanol anddiluted with water (10 mL). This mixture was acidified with 10%hydrochloric acid solution to pH 2-3. The mixture was extracted withethyl acetate (2×10 mL). The combined ethyl acetate extracts were washedwith brine (I×10 mL), dried (Na₂SO₄), filtered and concentrated in vacuoto give the desired stereoisomer of beraprost (314d) as foamy solid(0.700 g). This acid was used out as such for potassium salt formation

Synthesis of Potassium Salt of Beraprost (314d)

A 100-mL, two-necked, round-bottom flask equipped with a magneticstirrer and a thermometer was charged with beraprost (314d) (0.500 g)and ethyl acetate (15 mL). This mixture was warmed to 75-80° C. toobtain a clear solution. To this clear solution, potassium hydroxide(0.066 g) in ethanol (3.0 mL) was added and stirred for few minutes at75-80° C., then the mixture was allowed to cool to ambient temperatureover a period of approximately 2 h. At ambient temperature, theprecipitated product was isolated by filtration and washed with ethanol.The product was transferred from Buchner funnel to a glass dish forair-drying overnight in a fume hood to yield free flowing white-solidsalt of beraprost (0.420 g); the solid was crystallized from ethanol andwater to obtain pure stereoisomer of beraprost potassium salt, chiralpurity 99.6% by Chiral HPLC; mp 270-272° C. (dec.); Required: C=66.03;H=6.70; Found C=65.82; H=6.67. The compound was characterized byspectral data.

Example 6 Synthesis of Side Chain with Chiral Methyl

Step 1: A 2-L, three-necked, round-bottom flask equipped with amechanical stirrer and an argon inlet-outlet adapter connected to abubbler was charged with a solution of(R)-(+)-4-(diphenylmethyl)2-oxazolidinone (2, 25 g in 200 mL of THF).The solution was cooled to −78° C. under argon. To the solution wasadded n-butyllithium in hexanes (1.6 M, 64.80 mL) drop wise at −78° C.over a period of 45-60 minutes. The reaction mixture was stirred at −78°C. for 30-45 min. Then, propionyl chloride (20.10 g dissolved in 30-50mL of dry THF) was added drop wise at −78° C. over 15-30 min. Themixture was stirred at −78° C. for 1-2 h (Note 1). The reaction mixturewas quenched with saturated solution of ammonium chloride (15 mL) at−78° C. to −60° C. and then allowed to warm-up to ambient temperature.An additional amount of ammonium chloride (100 mL) was added to thereaction mixture at ambient temperature and the mixture was swirled inseparatory funnel. The organic layer was separated from aqueous layer.The aqueous phase was extracted with MTBE (2×100 mL). The combinedorganic phases were washed with aqueous NaHCO₃ (100 mL), brine (100 mL),then dried over anhydrous Na₂SO₄ followed by filtration. The filtratewas concentrated in vacuo to afford crude solid product (30.38 g,quantitative).

Step 2: A 500-mL, round-bottom flask equipped with a magnetic stirrerand an argon inlet-outlet adapter connected to a bubbler was chargedwith 1-bromo-2-butyne (23.21 g) and THF (100-120 mL) under argon at roomtemperature. To the solution of 1-bromo-2-butyne, sodium iodide (27.90g) was added. The reaction mixture was stirred for 2-3 h at ambienttemperature. The suspension was filtered using a Whatmann filter paperNo. 50 and the solid washed with dry THF (15-30 mL). The filtratecontaining l-iodo-2-butyne in THF was used in the next step.

Step 3: A 2-L, three-necked, round-bottom flask equipped with amechanical stirrer and an argon inlet-outlet adapter connected to abubbler was charged with a solution of NaN(SiMe₃)₂ (1.0 M, 174 mL). Tothis solution was added a solution of oxazolidinone (36 gin 50-80 mL ofTHF) drop wise at −78° C. After the mixture was stirred at −78° C. for60-120 min, l-iodo-2-butyne (freshly prepared in THF in step one) wasadded drop wise at −78° C. over a period of 45-60 min using a droppingfunnel. The mixture was stirred for 2 h, and then quenched the reactionmixture with acetic acid (11 mL) at −78° C. The mixture was allowed towarm to ambient temperature and aqueous sodium chloride (500-750 mL) wasadded. The organic layer was separated from the aqueous layer. Theaqueous phase was extracted with MTBE (3×400 mL). The combined organicphases were washed with aqueous NaHCO₃ (100 mL), then dried overanhydrous Na₂SO₄, followed by filtration. The filtrate was concentratedin vacuo to ⅕th of the total volume. Ethanol (150 mL) was added and themixture concentrated in vacuo to a slurry. An additional amount ofethanol (200 mL) was added and then concentrated again in vacuo to aslurry in order to remove other solvents carried over from reaction andwork-up.

Crystallization: To the resulting slurry, ethanol 300-350 mL was addedand mixture was heated to obtain a clear solution. The clear solutionwas allowed to cool slowly to ambient temperature. The resulting solidwas collected by filtration and washed with a solution of ethanol inhexanes (50%, 50-150 mL). The solid product was transferred to glasstray and air-dried to afford white, crystalline oxazolidinone (24.74 g,59%), mp 128-130° C.

Example 7 Synthesis of Phosphonate Side Chain

Step 1: A 500-mL, round-bottom flask equipped with a mechanical stirrerwas charged with a solution of oxazolidinone 8 (24.50 g) in THF (295mL), water (114 mL) and LiOH (2.273 g). The mixture was stirred atambient temperature for 16-24 h. A saturated solution of sodiumbicarbonate (50-75 mL) was added to the reaction mixture slowly whilestirring. The reaction mixture was extracted with MTBE (5×100 mL) toremove the chiral auxiliary and impurities. The aqueous layer wasadjusted to pH 3-4 by addition of dilute hydrochloric acid and extractedwith MTBE (3×150 mL). The combined organic layers were washed with brine(1×150 mL), and then dried over anhydrous Na₂SO₄, followed byfiltration. The filtrate was concentrated in vacuo to give crudecarboxylic acid (6.4 g, 74.5%).

Step 2: A 500-mL, round-bottom flask equipped with a magnetic stirrerwas charged with carboxylic acid (10) (6.35 g),2-chloro-4,6-dimethoxy-1,3,5-triazine (11.93 g), and N-methylmorpholine(14.6 mL) in THF (70-100 mL). The suspension was stirred at ambienttemperature for 1-2 h. After stirring for 1-2 h, MeO(Me)NH.HCl (5.89 g)was added and the mixture stirred at RT overnight (16-18 h). To thereaction mixture, hexane (50-100 mL) was added. The slurry was filteredthrough a pad of Celite. The Celite bed was washed with hexanes (50-100mL). The filtrate was concentrated in vacuo to afford crude amide (11).The crude product was dissolved in hexane (50-100 mL) and filtered againthrough a pad of Celite in order to remove suspended solid impurities.The Celite bed was washed with hexanes (50-100 mL). The filtrate wasconcentrated in vacuo to afford crude product. The crude product waspurified by silica gel column chromatography (gradient: EtOAc/hexanes,5-25%) to afford Weinreb amide (7.2 g, 85%) as a colorless oil with a98.42% purity (by chiral HPLC).

Step 3: A 500-mL, three-necked, round-bottom flask equipped with amagnetic stirrer and an argon inlet-outlet adapter connected to abubbler was charged with a solution of dimethyl methylphosphonate (A)(13.00 g) in THF (50 mL) followed by drop wise addition of n-BuLi (1.6 Min hexanes, 52.50 mL) at −78° C. using a dropping funnel. The mixturewas stirred at −78° C. for 1 h and then a solution of amide 11 (7.10 g)in THF (20-30 mL) was added over a period of 30-45 minutes using adropping funnel. After complete addition, the mixture was stirred at−78° C. for 2 h, then the reaction was quenched with aqueous NH₄Cl (100mL). The mixture was allowed to warm-up to ambient temperature. Themixture was extracted with ethyl acetate (3×75 mL). The combined organiclayers were washed with brine (1×50 mL), then dried over anhydrousNa₂SO₄, followed by the filtration. The filtrate was concentrated invacuo to afford crude product. The crude product was purified by columnchromatography (gradient, EtOAc/hexanes, 10-100%) to afford(S)-3-methyl-2-oxohept-5-ynylphosphonic acid dimethyl ester (9.218 g,95%).

* * *

All of the publications, patent applications and patents cited in thisspecification are incorporated herein by reference in their entirety.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the present invention is not so limited. It willoccur to those of ordinary skill in the art that various modificationsmay be made to the disclosed embodiments and that such modifications areintended to be within the scope of the present invention.

What is claimed is:
 1. A process for preparing a compound of thefollowing formula:

wherein R^(1a) represents a cation, H, or C₁₋₁₂ alkyl, comprising thesteps of: (1) performing a cycloaddition reaction on the compound of thefollowing formula:

wherein in R^(2a) and R⁶ independently represent hydroxy protectinggroups, with a compound of the following formula:

wherein R⁷ represents C₁₋₆ alkoxy or C₁₋₁₂ alkyl-COOR⁹, where R⁹represents C₁₋₃ alkyl and R⁸ represents halide or H to form a compoundof the following formula:

wherein R^(2a), R⁶, R⁷, and R⁸ are each defined above; (2) aromatizingthe cyclodiene of formula (IV) to form the aromatic product of thefollowing formula:

(3) Reducing the ester of the compound of formula (V) to a benzylalcohol and oxidation of benzyl alcohol to an aldehyde followed byaddition of a carbon to said aldehyde to form an alkyne resulting in acompound of the following formula:

(4) coupling the terminal alkyne with N₂CH₂CO₂R^(1a), wherein R^(1a)represents a C₁₋₁₂ alkyl followed by hydrogenation of the alkyne to itscorresponding alkane followed by deprotection of the hydroxyl protectivegroups to form a compound of the following formula:

wherein R^(1a) represents a cation, H, or C₁₋₁₂ alkyl.
 2. The process ofclaim 1, wherein the compound of formula (VII) is produced as asubstantially pure single isomer.